I cant address the bunting deal, because thats a struck ball, whereas here its a D3K swinging.
Cite the rule where the B/R is 'already out' if he does not immediately start running to 1B. Neither desertion nor abandonment apply here..he has not 'left the dirt circle'. TWP: if there were no runners, D3K, and the B/R stood there and the defense retrieved the ball but made no play - how long would you allow the B/R to stand there before calling him out for 'no attempt?' 10 seconds? 60 seconds? 5 minutes?
I just dont think you can say that because the B/R didnt instantly leave for 1B (or desert), that
alone makes him out...its not supported by rule. Unless I'm wrong
So, to me, at the time the INT occurred, the batter is now a B/R, who is still 'alive' (not out) for purposes of the play. By rule, its the same as if he was 1/2 up the baseline to 1B, and interfered with a throw to retire R3 at the plate. The fact that the B/R is still located in the box at the time of INT is irrelevant to his status as a batter-runner.
Yes, the INT is a dead ball, but the rule explicity states that the penalty is that the interferer is out (BR in this case) and the runner (R3) returned to TOI base. This 'cant get to 1B on a dead ball' is a chimera...he's already out for his interference, because when he struck at the pitch, he ceased to be a batter instantly. He's now a B/R, and different INT rules apply.